What Are Internet Memes on Facebook?

Lately on Facebook I've been reading a lot about some images called "Memes". Sometimes my friends post a meme on their Facebook walls and they laugh and comment a lot but I feel left out, because I don't think they're funny. I know there are several "meme specialized" Internet sites but I kinda get lost in them. What are Internet memes? How do I post them on Facebook? Can I create them on the Internet or do I have to download image editing software?

Internet Memes are images, ideas or styles that passes from person to person, commonly in Internet specialized sites. This Memes usually become viral with the new mass communication services such as social networks (Facebook, Twitter). Commonly people from all over the world share Internet Memes which can be adapted or personalized from language, country, personal groups, etc.
Richard Dawkins created the term in his 1976 book "The Selfish Gene", as an attempt to explain the way cultural information spreads.
Most people create or edit them on image editing software like Photoshop, Corel, or even Paint.
You can also create them on Internet sites like Meme Generator, which allows to chose a Meme and write your own jokes or puns, and lets you publish them on Facebook or other social networks.
If you don't to create them, just share them, most of the Internet Meme sites have "Facebook share" buttons that eases the sharing process.